Mercury Force 1996 115 Tachometer not working

[dswanson79]

Hi I bought and replaced my tachometer thinking it was a bad tach however the new one is not working either. When the power is turned on the needle does move forward just a hair. Any help would be greatly appreciated.

 

[CharlieB]

Re: Mercury Force 1996 115 Tachometer not working

Ussually a dead tach is caused by a bad rectifier.

Check battery voltage with engine OFF then again running at 2000 RPM or more while on the water. I don't recommend testing on the hose, most will not supply adequate water flow.

If battery voltage does not rise then remove the rectifier and ohms test each yellow to the red then reverse polarity of your leads and test again. The grey wire is your tach trigger.

You should have continuity in one direction y/r but not the reverse.

Post your results.

 

[dswanson79]

Re: Mercury Force 1996 115 Tachometer not working

I took the rectifier / voltage regulator off the motor and when I turned it over it was obvious that it had been fried. I was able to purchase a brand new regulator on ebay for about $70. Just got back from a short trip on the water and the tach works great as well as the charging system. Thanks again for the help!!!

 

[Stamey]

Re: Mercury Force 1996 115 Tachometer not working

So I think I am in the same boat. Just found this thread by search and am following the directions. Tach got jumpy then stopped working. My rectifier looks about like the one pictured, in that there are really brown spots inside the potting, on the circuit board. Problem though is it does charge once you are above an idle. At idle it's about 12v, and when you rev it up the voltage jumps to 14.
I measured resistance between the single red wire and the 2 yellow wires, one at a time, and in reverse. In either direction, Y1 to R is 45K ohms, where Y2 to R is 1.1M ohms. So since there is resistance in both directions I suppose the diodes are bad?
Do I call this rectifier bad?

Thanks,
Chris

 

[CharlieB]

Re: Mercury Force 1996 115 Tachometer not working

Yes, 45 Ohms is way too low and is allowing current to flow backwards while the engine is turned off, draining the battery and causing the stator coils to act as heaters.

Disconnect the battery and replace the rectifier before it causes damage to the stator.

 

[Dave1027]

Re: Mercury Force 1996 115 Tachometer not working

I took the rectifier / voltage regulator off the motor and when I turned it over it was obvious that it had been fried. I was able to purchase a brand new regulator on ebay for about $70. Just got back from a short trip on the water and the tach works great as well as the charging system. Thanks again for the help!!!

Which begs the question: What caused it to fry? I guess any electronic component can fry for no reason but not usually. Maybe a battery or connection malfunction?